1. Field of the Invention
The present invention relates to acrylonitrile copolymers and polyacrylonitriles free from comonomers, which have improved dye absorption for basic dyes, and to a process for the preparation of polyacrylonitrile and of copolymers predominantly containing acrylonitrile by means of polymerisation in aliphatic hydrocarbons in the presence of a redox catalyst system.
2. Discussion of Prior Art
It is well known that the preparation of polyacrylonitrile and of copolymers predominantly containing acrylonitrile, which may be used for example for spinning into fibres of the acrylic or modacrylic type, or as thermoplastic materials for the production of foils or hollow bodies such as bottles, is carried out mainly in aqueous media. This method of production comprises several stages including distillations for working up the polymer, and complete recycling of all the components of the system is therefore difficult and above all entails high energy consumption.
In addition, acrylonitrile polymers obtained from aqueous media generally require the use of ionic comonomers in order to obtain good dye absorption with cationic or anionic dyes. This frequently leads to ecological problems.
It is also known to polymerise acrylonitrile in aliphatic and aromatic hydrocarbons, using azo catalysts (Faserforschung and Textiltechnik 12 (1961), 5, page 208 and Faserforschung and Textiltechnik 15 (1965), page 331).
It has generally been found, however, that when polymerisation is carried out in such systems, the use of azo catalysts and peroxidic compounds alone, that is without the addition of activating components, requires relatively high reaction temperatures which causes severe discolouration of the products and great molecular non-uniformity. Another disadvantage of this particular method is that the ionic dye comonomers normally used must be completely dispensed with because they are insoluble in the system, and therefore do not become chemically fixed in the course of polymerisation. This has a disadvantageous effect upon the colour characteristics of the polymers obtained and upon those of the shaped products manufactured from them.
Although it is known, having been described mainly for solvent-free polymerisation of vinyl chloride, that acceptable conversion ratios can still be obtained at substantially lower polymerisation temperatures by using a starter system consisting of an organic hydroperoxide, sulphur dioxide and a nucleophilic basic reagent, it is made quite clear that the basic component is essential. Its absence results in a severe loss in yield and due to the incorporation of sulphur dioxide in the polymer chain in the form of sulphone groups, it results in thermally unstable polymers. (Chem. Ing. No. 16, 43 (1971), page 941).
The catalyst system mentioned above cannot be used for the homopolymerisation and copolymerisation of acrylonitrile in aliphatic hydrocarbons because in these media, the reaction of sulphur dioxide with the proposed basic components results in the precipitation of a salt-type compound which interferes with the progress of polymerisation and has no activating effect.